The proposed research seeks to elucidate the connections and the intrinsic synaptic organization of the amphibian optic tectum, (including current source-density analysis and intracellular recordings). These studies are directed at understanding what information is encoded at successive stages of the visual system, how receptive fields of higher-order neurons are determined, and the extent to which they are influenced by presynaptic gating of the retinal input and by interactions with other non-visual inputs. A second goal of the proposed research seeks to elucidate some molecular mechanisms that might underlie the formation of retino-tectal synaptic connections during regeneration of the optic nerve, in particular, interactions which occur between molecules at the exploring tip of the growing axons, and the receptive surfaces of the neurons towards which they are growing. These studies will include histochemical and biochemical procedures for measuring neurotransmitter synthesis, and the use of labelled snake neurotoxins in studying receptor protein in cholinergic synapses. Information gained from these studies might provide useful insights into the mechanisms underlying synaptogenesis and neuronal specificity in this and other systems. BIBLIOGRAPHIC REFERENCES: Freeman, J. A. Patterns of convergence of afferents onto tectal neurons in Bufo marinus revealed by intracellular recording. Soc. for Research in Vision and Ophthalmology #6, 91 (1976). Oswald, R. E., and J. A. Freeman. Extracellular potassium changes associated with the control of retinotectal synaptic transmission in Bufo marinus. Soc. for Neurosciences, Vol. II, #1438 (1976).